Coherence protocol for distributed caches

ABSTRACT

The disclosure provides for a reactive cache coherence protocol that has efficiencies over proactive approaches. Rather than proactively performing remediation when a data item is invalidated, a destination endpoint checks cache coherence upon receiving an indication of a cache hit, and based at least on detecting a lack of coherence, performs a reactive remediation process. For example, the incoherence may be fixed by replacing, as a cached data item, a data block indicated by the cache hit with a replacement data block that triggered the cache hit.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.16/198,975, filed Nov. 23, 2018, entitled “Coherence Protocol forDistributed Caches”, the entirety of which is hereby incorporated byreference herein.

BACKGROUND

Cache coherence is the uniformity of shared resource data that ends upstored in multiple local caches. When different nodes in a multi-nodeprocessing architecture maintain caches of a common resource, problemsmay arise with incoherent data. For example, consider a scenario inwhich two different nodes (e.g., CPUs) have both cached a copy of aparticular data block (e.g., a memory block). If the first node altersits local copy of the data block, and the second node is left with aninvalid cache of the data block this results in a lack of coherence.Cache coherence manages conflicts by maintaining coherence of the datain the various multiple caches.

Another example is two nodes attempting to speed up networkcommunication by caching hashes of previously transferred files. When apreviously transferred file is modified or deleted, the cache on thedestination may be updated by monitoring writes to the file in question.However, updating the cache on the source would require a networkcommunication event, which consumes processing power and networkbandwidth. If the network message is not properly received andprocessed, the different caches would become incoherent.

Common proactive cache coherence management dictates that when a firstcache and a second cache become incoherent as a result of changes to thesecond cache, the changes are actively monitored and remediated byremoving the now-invalid data item from the first cache. Suchremediation work is wasted if the data item in the first cache is neverhit again. Additionally, if the data item is subsequently encountered,it is no longer available in the cache for use. Therefore, proactivecache coherence management may not provide efficient operation in somescenarios.

SUMMARY

This Summary is provided to introduce a selection of concepts in asimplified form that are further described below in the DetailedDescription. This Summary is not intended to identify key features oressential features of the claimed subject matter, nor is it intended tobe used as an aid in determining the scope of the claimed subjectmatter.

An exemplary system for maintaining cache coherence comprises ateleporter configured to indicate a cache hit, and a destinationendpoint coupled to the teleporter, wherein the destination endpoint isconfigured to, based at least on receiving an indication of the cachehit from the teleporter, check cache coherence and, based at least ondetecting a lack of coherence, perform a reactive remediation process.

BRIEF DESCRIPTION OF THE DRAWINGS

The present description will be better understood from the followingdetailed description read in the light of the accompanying drawings,wherein:

FIG. 1 illustrates a block diagram of an architecture for maintainingcache coherence, by implementing a coherence protocol for distributedcaches, while transmitting a data block, according to an exampleembodiment;

FIG. 2A illustrates the architecture of FIG. 1 in which a subsequenttransmittal of the same data block results in a cache hit withcoherency, according to an example embodiment;

FIG. 2B illustrates the architecture of FIG. 1 in which a subsequenttransmittal of the same data block results in a cache hit with a lack ofcoherency, according to an example embodiment;

FIG. 3 illustrates the architecture of FIG. 1 in which a furthersubsequent transmittal of the same data block results in a cache hit,according to an example embodiment;

FIG. 4 illustrates a flowchart corresponding to the activity indicatedin FIG. 1, according to an example embodiment;

FIG. 5 illustrates a flowchart corresponding to the activity indicatedin FIGS. 2A and 2B, according to an example embodiment;

FIG. 6 illustrates a flowchart corresponding to the activity indicatedin FIG. 3, according to an example embodiment;

FIG. 7 illustrates a flowchart showing a method for maintaining cachecoherence, according to an example embodiment that may be used with thearchitecture of FIG. 1;

FIG. 8 illustrates a flowchart showing another method for maintainingcache coherence, according to an example embodiment that may be usedwith the architecture of FIG. 1; and

FIG. 9 illustrates a block diagram of a computing device that employscaching, and that may be used with the architecture of FIG. 1, accordingto an example embodiment.

DETAILED DESCRIPTION

Various aspects of the systems and methods described herein provide atleast a reactive cache coherence protocol for distributed caches thathas efficiencies over proactive approaches. Rather than proactivelyperforming remediation when a data item is invalidated, a destinationendpoint checks cache coherence upon receiving an indication of a cachehit, and based at least on detecting a lack of coherence, performs areactive remediation process. For example, the incoherence may be fixedby replacing, as a cached data item, a data block indicated by the cachehit with a replacement data block that triggered the cache hit.

In this manner, the disclosure is able to maintain cache coherence byimplementing a coherence protocol for distributed caches. Aspects of thedisclosure provide for a reactive cache coherence protocol that hasefficiencies over proactive approaches. Additionally, the disclosure isoperable with cached disk images, memory pages, and/or database pages,as well as variable size blocks.

The disclosure operates in an unconventional manner by performing areactive remediation process, rather than a proactive remediationprocess. This improves the functioning of the underlying computingdevice by reducing the amount of remediation work to perform, savingcomputing resources and improving the user experience.

It should be understood that any of the examples herein arenon-limiting. As such, the present disclosure is not limited to anyparticular embodiments, aspects, concepts, structures, functionalitiesor examples described herein. Rather, the present disclosure may be usedin various ways that provide benefits and advantages in computingsystems including virtualized computing environments.

FIG. 1 illustrates a block diagram of an architecture 100 formaintaining cache coherence, by implementing a coherence protocol fordistributed caches, while transmitting a data block. In some examples,architecture 100 is able to perform deduplication of disk images duringnetwork transfer. FIG. 1 should be viewed along with FIG. 4, whichillustrates a flowchart 400 corresponding to the activity indicated inFIG. 1.

Architecture 100 comprises a source node 120, a network 126, and adestination node 130. Coherence is to be maintained between node 120 anddestination node 130. Source node 120 has a source endpoint 122 andsource storage location 124. Destination node 130 has a destinationendpoint 132, a first destination storage location 134, a seconddestination storage location 136, a third destination storage location138, a private cache 146, and a teleporter 140, all coupled todestination endpoint 132. In some examples, storage locations 124, 134,136, and 138 comprise disk images. Destination node 130 further has ashort-term cache 142 and a long-term cache 144, both coupled toteleporter 140. Teleporter 140 is configured to indicate a cache hit todestination endpoint 132. Destination endpoint 132 is configured to,based at least on receiving an indication of a cache hit from teleporter140, check cache coherence. Destination endpoint 132 is furtherconfigured to, based at least on detecting a lack of coherence, performa reactive remediation process using a data block in a destinationstorage location.

In operation 402 (of FIG. 4) a data block D1 in source storage location124 is selected to be transmitted to destination node 130 over network126 using source endpoint 122, and is sent as message 101. In someexamples, data block D1 is a memory page or a portion of memory. Datablock D1 need not be a fixed size, but may vary in size, in someexamples.

Source endpoint 122 hashes data block D1 to generate a data hash valueH1 in operation 404. In some examples, data hash value H1 comprises a256-bit hash, although different hash lengths may be used. Someconsiderations include that the hash value is sufficiently long tominimize the likelihood of a collisions, and that the calculation timebe reasonably efficient. So, in some examples, the entirety of D1 maynot be hashed. Teleporter 140 is configured to receive data hash valuesand receives data hash value H1 over network 126 as message 102, inoperation 406. Based at least on teleporter 140 receiving data hashvalue H1, teleporter 140 searches within short-term cache 142 (as afirst portion of message 103) and possibly also within long-term cache144 for data hash value D1 and a matching block location, in operation408. However, teleporter 140 cannot find data hash value H1, soteleporter 140 stores data hash value H1 as a second portion of message103, in operation 410. Data block D1 is requested from source endpoint122 via message 104, in operation 412. Source endpoint 122 thentransmits data block D1 to destination endpoint 132 as message 105, anddestination endpoint 132 receives data block D1 in operation 414.

Destination endpoint 132 then copies data block D1 received from sourceendpoint 122 to the destination storage location 134 as message 106,thereby storing data block D1, in operation 416. Additionally,destination endpoint 132 informs teleporter 140 of the location (A1) ofdata block D1 in destination storage location 134 as message 107, inoperation 418. Teleporter 140 stores block location A1 in short-termcache 142 along with data hash value H1 as a third portion of message103, in operation 420.

FIG. 2A illustrates architecture 100 of FIG. 1 in which a subsequenttransmittal of data block D1 results in a cache hit with coherency. FIG.2A should be viewed along with FIG. 5, which illustrates a flowchart 500corresponding to the activity indicated in FIGS. 2A and 2B. In operation402 (of FIG. 5) data block D1 in source storage location 124 is againselected to be transmitted to destination node 130 over network 126using source endpoint 122, and is sent as message 201. Source endpoint122 hashes data block D1 to generate data hash value H1 in operation 404(which matches data hash value H1 generated in operation 404 of FIG. 4).Teleporter 140 receives data hash value H1 over network 126 as message202, in operation 406. In operation 408, based at least on teleporter140 receiving data hash value H1, teleporter 140 searches withinshort-term cache 142 for data hash value H1 and matching block locationA1, and also possibly in long-term cache 144. The results of the searchare determined in operation 510. If teleporter 140 does not find datahash value H1 and matching block location block location A1, operationmoves to operation 410 of flow chart 400 (if FIG. 4).

In operation 512, teleporter 140 finds data hash value H1 and matchingblock location block location A1 and receives them from short-term cache142 as message 203. Based at least on teleporter 140 finding data hashvalue H1 and matching block location block location A1 in short-termcache 142, teleporter 140 promotes data hash value H1 from short-termcache 142 to long-term cache 144 as the first portion of message 204, inoperation 514. Also based at least on teleporter 140 finding data hashvalue H1 and matching block location block location A1 in short-termcache 142, teleporter 140 indicates a cache hit to destination endpoint132 as message 205, in operation 516. In some examples, indicating acache hit comprises, based at least on finding matching block locationA1, indicating to destination endpoint 132 data hash value H1 andmatching block location A1. In operation 518, destination endpoint 132receives the indication of the cache hit from teleporter 140. In someexamples, receiving, at a destination endpoint, an indication of a cachehit from a teleporter comprises receiving, from the teleporter, a datahash value and a matching block location.

Based at least on receiving the indication of the cache hit, destinationendpoint 132 begins checking cache coherence. Checking cache coherencecomprises operations 520-524. In the scenario depicted in FIG. 2A, datablock D1 is intact and has not changed. In operation 520, destinationendpoint 132 retrieves data block D1 found at matching block location A1in destination storage location 134, as message 206. In operation 522,destination endpoint 132 generates a check hash value H1 c for datablock D1 found at matching block location A1 in destination storagelocation 134. Check hash value H1 c will use the same hash function aswas used to generate the data hash value, so in some examples, the checkhash value comprises a 256-bit hash. In operation 524, destinationendpoint 132 compares check hash value H1 c with data hash value H1.Because, in this scenario, data block D1 is intact and has not changed,decision operation 526 indicates that check hash value H1 c matches datahash value H1. This is an indication of coherence. The lack of coherencescenario is described in relation to FIG. 2B.

Based at least on check hash value H1 c matching data hash value H1,destination endpoint 132 copies data block D1 found at matching blocklocation Al to destination storage location 136 as message 207, inoperation 528. Also based at least on check hash value H1 c matchingdata hash value H1, destination endpoint 132 copies data block D1 foundat matching block location A1 to private cache 146 (in a new locationA2) as message 208, in operation 530. Additionally, destination endpoint132 informs teleporter 140 of the new block location A2 of data block D1in private cache 146 as message 209, in operation 532. Teleporter 140stores block location A2 in long-term cache 144 along with data hashvalue H1 as a second portion of message 204, in operation 534.

Turning now to FIG. 2B, and still with reference to FIG. 5, in thisscenario, data block D1 has been changed. The data block copy indestination storage location 134 is labeled as D1 a and the check hashvalue is labeled as H2 c to indicate that they are no longer the same asin FIG. 2A. Thus, decision operation 526 indicates that check hash valueH2 c does not match data hash value H1. This is an indication of lack ofcoherence. Based at least on detecting a lack of coherence, architecture100 performs a reactive remediation process using data block D1 and/ordata block D1 a.

Based at least on check hash value H2 c not matching data hash value H1,data block D1 is requested from source endpoint 122 via message 210, inoperation 536. Source endpoint 122 then transmits data block D1 todestination endpoint 132 as message 211, and destination endpoint 132receives data block D1 in operation 538. Also based at least on checkhash value H2 c not matching data hash value H1, destination endpoint132 copies data block D1 received from source endpoint 122 todestination storage location 136 as message 212, in operation 540.Destination endpoint 132 then copies data block D1 received from sourceendpoint 122 to private cache 146 (in a new location A2) as message 213,in operation 542. Additionally, destination endpoint 132 informsteleporter 140 of the new block location A2 of data block D1 in privatecache 146 as message 209, in operation 544. Teleporter 140 stores blocklocation A2 in long-term cache 144 along with data hash value H1 as asecond portion of message 204, in operation 546. Operations 536-546together comprise, based at least on detecting a lack of coherence,performing a reactive remediation process. In this manner theremediation process comprises replacing, as a cached data item, datablock D1 a indicated by the cache hit with replacement data block D1that triggered the cache hit.

It should be noted that the end result of the scenarios depicted in bothFIGS. 2A and 2B are the same: data hash value H1 and block location A2are in long-term cache 144, and data block D1 is in private cache 146.That is, independently of whether decision operation 526 detected cachecoherence or lack of coherence, the end result was still cachecoherence. Coherence is not checked until a cache hit was experienced,and incoherence is detected by comparing hashes. Incoherence is fixed byreplacing the cache item that was invalidated with the new item that hascaused the cache hit. This is a reactive, as-needed remediationapproach, which may be contrasted with proactive invalidation.

FIG. 3 illustrates architecture 100 of FIG. 1 in which a furthersubsequent transmittal of data block D1 results in a cache hit. FIG. 3should be viewed along with FIG. 6, which illustrates a flowchart 600corresponding to the activity indicated in FIG. 3. In operation 402 (ofFIG. 6) data block D1 in source storage location 124 is yet againselected to be transmitted to destination node 130 over network 126using source endpoint 122, and is sent as message 301. Source endpoint122 hashes data block D1 to generate data hash value H1 in operation404. Teleporter 140 receives data hash value H1 over network 126 asmessage 302, in operation 406. Based at least on teleporter 140receiving data hash value H1, teleporter 140 searches within long-termcache 144, and possibly also within short-term cache 142 for data hashvalue D1 and a matching block location, in operation 408.

In operation 512, teleporter 140 finds data hash value H1 and matchingblock location block location A2 and receives them from long-term cache144 as message 303. Based at least on teleporter 140 finding data hashvalue H1 and matching block location block location A2 in long-termcache 144, teleporter 140 indicates a cache hit to destination endpoint132 as message 304, in operation 516. In operation 518, destinationendpoint 132 receives the indication of the cache hit from teleporter140.

Because matching block location block location A2 indicates a locationwithin private cache 146, and the contents of private cache 146 areexpected to remain unchanged, in some examples, checking coherency bycomparing hash values may not be needed. In operation 616, destinationendpoint 132 retrieves data block D1 found at matching block location A2in private cache 146, as message 305. In operation 618, destinationendpoint 132 then copies data block D1 from private cache 146 (found atmatching block location A2) to destination storage location 138, asmessage 306.

FIG. 7 illustrates a flowchart 700 showing a method for maintainingcache coherence, that may be used with the architecture of FIG. 1.Operation 702 includes receiving, at a destination endpoint, anindication of a cache hit from a teleporter. Operation 704 includes,based at least on receiving the indication of the cache hit, checkingcache coherence. Operation 706 includes, based at least on detecting alack of coherence, performing a reactive remediation process. In someexamples, performing a reactive remediation process in operation 706comprises replacing, as a cached data item, a data block in a firstdestination storage location indicated by the cache hit with areplacement data block that triggered the cache hit.

FIG. 8 illustrates a flowchart 800 showing a method for maintainingcache coherence, that may be used with the architecture of FIG. 1.Flowchart 800 combines the operations of flow charts 400, 500, and 600.In operation 402 a data block D1 is selected to be transmitted todestination node 130. Source endpoint 122 hashes data block D1 inoperation 404. Teleporter 140 receives data hash value H1 over network126 from source endpoint 122 in operation 406. Based at least onteleporter 140 receiving data hash value H1, teleporter 140 searcheswithin short-term cache 142 and/or within long-term cache 144 for datahash value D1 and a matching block location, in operation 408. Theresults of the search are determined in operation 510.

If teleporter 140 does not find data hash value H1 and a matching blocklocation block location, operation moves storing data hash value H1, inoperation 410. Data block D1 is requested from source endpoint 122, inoperation 412. Source endpoint 122 then transmits data block D1 todestination endpoint 132, and destination endpoint 132 receives datablock D1 in operation 414. Destination endpoint 132 then copies datablock D1 to the destination storage location 134, thereby storing datablock D1, in operation 416. Additionally, destination endpoint 132informs teleporter 140 of the location of data block D1, in operation418. Teleporter 140 stores block location A1 in short-term cache 142along with data hash value H1, in operation 420.

If, however, data hash value H1 and a matching block location blocklocation (A1 or A2) are present in a cache, teleporter 140 finds them inoperation 512. If the matching block location block location had been inshort-term cache 142, teleporter 140 promotes data hash value H1 fromshort-term cache 142 to long-term cache 144, in operation 514.Teleporter 140 indicates the cache hit to destination endpoint 132 inoperation 516, and destination endpoint 132 receives the indication ofthe cache hit from teleporter 140 in operation 518. In some examples,receiving, at a destination endpoint, an indication of a cache hit froma teleporter comprises receiving, from the teleporter, a data hash valueand a matching block location.

In decision operation 802, teleporter determines whether the matchingblock location block location is within private cache 146. If so, thenchecking coherency by comparing hash values may not be needed. Inoperation 616, destination endpoint 132 retrieves data block D1 (foundat matching block location A2) from private cache 146. In operation 618,destination endpoint 132 then copies data block D1 from private cache146 to destination storage location 138.

Operations 520-546 are as previously described for FIG. 5. Operations536-546 together comprise, based at least on detecting a lack ofcoherence, performing a reactive remediation process. In this manner theremediation process comprises replacing, as a cached data item, datablock D1 a indicated by the cache hit with replacement data block D1that triggered the cache hit.

FIG. 9 illustrates a block diagram 900 of a computing device 902 thatemploys caching, and that may be used with the architecture of FIG. 1.With reference to FIG. 1, computing device 902 may be used for any ofsource node 120, source endpoint 122, source storage location 124,destination node 130, destination endpoint 132, first destinationstorage location 134, second destination storage location 136, thirddestination storage location 138, private cache 146, teleporter 140,short-term cache 142, and a long-term cache 144.

Computing device 902 has at least a processor 904 and a memory area 906that holds program code 908, a cache area 920, and other logic andstorage 922. Memory area 906 is any device allowing information, such ascomputer executable instructions and/or other data, to be stored andretrieved. For example, memory area 906 may include one or more randomaccess memory (RAM) modules, flash memory modules, hard disks,solid-state disks, and/or optical disks. Program code 908 comprisescomputer executable instructions, and computer executable componentscomprising source endpoint code 910, destination endpoint code 912,teleporter code 914, network communication code 916, and cachemanagement code 918. Source endpoint code 910 enables computing device902 to operate as source endpoint 122. Destination endpoint code 912enables computing device 902 to operate as destination endpoint 132.Teleporter code 914 enables computing device 902 to operate asteleporter 140. Network communication code 916 may be used whencomputing device 902 is operating as any of source endpoint 122,destination endpoint 132, and teleporter 140. Cache management code 918may be used when computing device 902 is operating as either ofdestination endpoint 132 and teleporter 140. Cache area 920 may hold anyof short-term cache 142, long-term cache 144, and private cache 146. Asillustrated, any of data block D1, data block D1 a, data hash value H1,check hash value H1, block location A1, and block location A2, may be inmemory area 906.

An input/output (I/O) module 924 permits communication over network 126to a remote node 932, which may be another manifestation of computingdevice 902. A storage location 934, coupled to computing device 902, maybe any of source storage location 124, destination storage location 134,destination storage location 136, and third destination storage location138, and/or may hold any of private cache 146, short-term cache 142, andlong-term cache 144.

Computing device 902 represent any device executing instructions (e.g.,as application programs, operating system functionality, or both) toimplement the operations and functionality described herein. Computingdevice 902 may include any portable or non-portable device including amobile telephone, laptop, tablet, computing pad, netbook, gaming device,portable media player, desktop personal computer, kiosk, and/or tabletopdevice. Additionally, computing device 902 may represent a group ofprocessing units or other computing devices, such as in a cloudcomputing system or service. Processor 904 may include any quantity ofprocessing units and may be programmed to execute any components ofprogram code 908 comprising computer executable instructions forimplementing aspects of the disclosure. In some embodiments, processor904 is programmed to execute instructions such as those illustrated inthe figures.

Additional Examples

An example system for maintaining cache coherence may comprise: ateleporter configured to indicate a cache hit; a first destinationstorage location; and a destination endpoint coupled to the teleporterand the first destination storage location, the destination endpointconfigured to: based at least on receiving an indication of the cachehit from the teleporter, check cache coherence; and based at least ondetecting a lack of coherence, perform a reactive remediation processusing a data block in the first destination storage location.

Another example system for maintaining cache coherence may comprise: ateleporter configured to indicate a cache hit; a first destinationstorage location; and a destination endpoint coupled to the teleporterand the first destination storage location, the destination endpointconfigured to: based at least on receiving an indication of the cachehit from the teleporter, check cache coherence; and based at least ondetecting a lack of coherence, perform a reactive remediation process tomaintain cache coherency by replacing, as a cached data item, a datablock in the first destination storage location indicated by the cachehit with a replacement data block that triggered the cache hit.

An exemplary method of maintaining cache coherence may comprise:receiving, at a destination endpoint, an indication of a cache hit froma teleporter; based at least on receiving the indication of the cachehit, checking cache coherence; and based at least on detecting a lack ofcoherence, performing a reactive remediation process using a data blockin a first destination storage location.

Another exemplary method of maintaining cache coherence may comprise:receiving, at a destination endpoint, an indication of a cache hit froma teleporter; based at least on receiving the indication of the cachehit, checking cache coherence; and based at least on detecting a lack ofcoherence, performing a reactive remediation process to maintain cachecoherency by replacing, as a cached data item, a data block in a firstdestination storage location indicated by the cache hit with areplacement data block that triggered the cache hit.

One or more exemplary non-transitory computer storage media havingcomputer-executable instructions that, upon execution by a processor,may cause the processor to at least perform operations that comprise:receiving, from a source endpoint, a data hash value; based at least onthe teleporter receiving the data hash value, searching within a firstteleporter cache for the data hash value and a matching block location;receiving, at a destination endpoint, an indication of a cache hit froma teleporter, the indication of the cache hit comprising the data hashvalue and the matching block location; based at least on receiving theindication of the cache hit, generating a check hash value for a datablock found at the matching block location; comparing the check hashvalue with the data hash value; promoting the data hash value from ashort-term cache to a long-term cache; based at least on the check hashvalue matching the data hash value, copying the data block found at thematching block location to a first destination storage location andcopying the data block found at the matching block location to a privatecache; based at least on the check hash value not matching the data hashvalue, copying a data block received from the source endpoint to thefirst destination storage location and copying the data block receivedfrom the source endpoint to the private cache; and copying a data blockfrom the private cache to a second destination storage location.

Alternatively, or in addition to the other examples described herein,examples include any combination of the following:

-   -   the remediation process comprises: replacing, as a cached data        item, a data block indicated by the cache hit with a replacement        data block that triggered the cache hit;    -   receiving an indication of a cache hit from the teleporter        comprises receiving, from the teleporter, a data hash value and        a matching block location; and checking cache coherence        comprises generating a check hash value for a data block found        at the matching block location; and comparing the check hash        value with the data hash value;    -   the data hash value comprises a 256-bit hash;    -   the check hash value comprises a 256-bit hash;    -   a first teleporter cache coupled to the teleporter;    -   the first teleporter cache comprises a short-term cache;    -   the teleporter is further configured to receive the data hash        value;    -   receiving, at the teleporter, the data hash value;    -   based at least on the teleporter receiving the data hash value,        search within the first teleporter cache for the data hash value        and the matching block location;    -   indicating a cache hit comprises, based at least on finding the        matching block location, indicating to the destination endpoint        the data hash value and the matching block location;    -   a long-term cache coupled to the teleporter;    -   promoting the data hash value from the short-term cache to the        long-term cache;    -   a second destination storage location coupled to the destination        endpoint;    -   the destination endpoint is further configured to, based at        least on the check hash value matching the data hash value, copy        the data block found at the matching block location to the        second destination storage location;    -   the destination endpoint is further configured to, based at        least on the check hash value not matching the data hash value,        copy a data block received from a source endpoint to the second        destination storage location;    -   a private cache coupled to the destination endpoint;    -   the remediation process comprises copying a data block to the        private cache;    -   copying a data block to the private cache comprises, based at        least on the check hash value matching the data hash value,        copying the data block found at the matching block location to        the private cache;    -   copying a data block to the private cache comprises, based at        least on the check hash value not matching the data hash value,        copying a data block received from a source endpoint to the        private cache;    -   the teleporter receiving the data hash value comprises the        teleporter receiving the data hash value from the source        endpoint;    -   a third destination storage location coupled to the destination        endpoint;    -   the destination endpoint is further configured to copy a data        block from the private cache to the third destination storage        location; and    -   copying a data block from the private cache to a third        destination storage location.

Exemplary Operating Environment

The operations described herein may be performed by a computer orcomputing device. The computing devices comprise processors and computerreadable media. By way of example and not limitation, computer readablemedia comprise computer storage media and communication media. Computerstorage media include volatile and nonvolatile, removable andnon-removable media implemented in any method or technology for storageof information such as computer readable instructions, data structures,program modules or other data. Computer storage media are tangible,non-transitory, and are mutually exclusive to communication media. Insome examples, computer storage media are implemented in hardware.Exemplary computer storage media include hard disks, flash memorydrives, digital versatile discs (DVDs), compact discs (CDs), floppydisks, tape cassettes, and other solid-state memory. In contrast,communication media typically embody computer readable instructions,data structures, program modules, or other data in a modulated datasignal such as a carrier wave or other transport mechanism, and includeany information delivery media.

Although described in connection with an exemplary computing systemenvironment, examples of the disclosure are operative with numerousother general purpose or special purpose computing system environmentsor configurations. Examples of well-known computing systems,environments, and/or configurations that may be suitable for use withaspects of the disclosure include, but are not limited to, mobilecomputing devices, personal computers, server computers, hand-held orlaptop devices, multiprocessor systems, gaming consoles,microprocessor-based systems, set top boxes, programmable consumerelectronics, mobile telephones, network PCs, minicomputers, mainframecomputers, distributed computing environments that include any of theabove systems or devices.

Examples of the disclosure may be described in the general context ofcomputer-executable instructions, such as program modules, executed byone or more computers or other devices. The computer-executableinstructions may be organized into one or more computer-executablecomponents or modules. Generally, program modules include, but are notlimited to, routines, programs, objects, components, and data structuresthat perform particular tasks or implement particular abstract datatypes. Aspects of the disclosure may be implemented with any number andorganization of such components or modules. For example, aspects of thedisclosure are not limited to the specific computer-executableinstructions or the specific components or modules illustrated in thefigures and described herein. Other examples of the disclosure mayinclude different computer-executable instructions or components havingmore or less functionality than illustrated and described herein.

Aspects of the disclosure transform a general-purpose computer into aspecial purpose computing device when programmed to execute theinstructions described herein. The examples illustrated and describedherein as well as examples not specifically described herein but withinthe scope of aspects of the invention constitute exemplary means formaintaining cache coherence. For example, the elements illustrated inthe figures, such as when encoded to perform the operations illustratedin the figures, constitute exemplary means for checking cache coherencebased at least on receiving an indication of a cache hit from ateleporter, and exemplary means for performing a reactive remediationprocess using a data block in a first destination storage location basedat least on detecting a lack of coherence.

The detailed description provided above in connection with the appendeddrawings is intended as a description of a number of embodiments and isnot intended to represent the only forms in which the embodiments may beconstructed, implemented, or utilized. Although these embodiments may bedescribed and illustrated herein as being implemented in devices such asa server, computing devices, or the like, this is only an exemplaryimplementation and not a limitation. As those skilled in the art willappreciate, the present embodiments are suitable for application in avariety of different types of computing devices, for example, PCs,servers, laptop computers, tablet computers, etc.

The term “computing device” and the like are used herein to refer to anydevice with processing capability such that it can execute instructions.Those skilled in the art will realize that such processing capabilitiesare incorporated into many different devices and therefore the terms“computer”, “server”, and “computing device” each may include PCs,servers, laptop computers, mobile telephones (including smart phones),tablet computers, and many other devices. Any range or device valuegiven herein may be extended or altered without losing the effectsought, as will be apparent to the skilled person. Although the subjectmatter has been described in language specific to structural featuresand/or methodological acts, it is to be understood that the subjectmatter defined in the appended claims is not necessarily limited to thespecific features or acts described above. Rather, the specific featuresand acts described above are disclosed as example forms of implementingthe claims.

While no personally identifiable information is tracked by aspects ofthe disclosure, examples have been described with reference to datamonitored and/or collected from the users. In some examples, notice maybe provided to the users of the collection of the data (e.g., via adialog box or preference setting) and users are given the opportunity togive or deny consent for the monitoring and/or collection. The consentmay take the form of opt-in consent or opt-out consent.

The order of execution or performance of the operations in examples ofthe disclosure illustrated and described herein is not essential, unlessotherwise specified. That is, the operations may be performed in anyorder, unless otherwise specified, and examples of the disclosure mayinclude additional or fewer operations than those disclosed herein. Forexample, it is contemplated that executing or performing a particularoperation before, contemporaneously with, or after another operation iswithin the scope of aspects of the disclosure.

It will be understood that the benefits and advantages described abovemay relate to one embodiment or may relate to several embodiments. Whenintroducing elements of aspects of the disclosure or the examplesthereof, the articles “a,” “an,” “the,” and “said” are intended to meanthat there are one or more of the elements. The terms “comprising,”“including,” and “having” are intended to be inclusive and mean thatthere may be additional elements other than the listed elements. Theterm “exemplary” is intended to mean “an example of.”

Having described aspects of the disclosure in detail, it will beapparent that modifications and variations are possible withoutdeparting from the scope of aspects of the disclosure as defined in theappended claims. As various changes may be made in the aboveconstructions, products, and methods without departing from the scope ofaspects of the disclosure, it is intended that all matter contained inthe above description and shown in the accompanying drawings shall beinterpreted as illustrative and not in a limiting sense.

1. (canceled)
 2. A method for maintaining cache coherence, the methodcomprising: receiving, at a destination endpoint, an indication of acache hit from a teleporter; based at least on receiving the indicationof the cache hit, checking cache coherence; and based at least ondetecting a lack of coherence, performing a reactive remediation processusing a data block in a first destination storage location.
 3. Themethod of claim 2, wherein the reactive remediation process comprises:replacing, as a cached data item, a data block indicated by the cachehit with a replacement data block that triggered the cache hit.
 4. Themethod of claim 2, wherein receiving, at the destination endpoint, theindication of the cache hit from the teleporter comprises: receiving,from the teleporter, a data hash value and a matching block location;and wherein checking cache coherence comprises: generating a check hashvalue for a data block found at the matching block location; andcomparing the check hash value with the data hash value.
 5. The methodof claim 4, wherein the data hash value comprises a 256-bit hash.
 6. Themethod of claim 4, wherein the check hash value comprises a 256-bithash.
 7. The method of claim 4, further comprising: based at least onthe check hash value matching the data hash value, copying the datablock found at the matching block location to a second destinationstorage location; and based at least on the check hash value notmatching the data hash value, copying a data block received from asource endpoint to the second destination storage location.
 8. Themethod of claim 4, wherein the remediation process comprises: promotingthe data hash value from a short-term cache to a long-term cache.
 9. Acomputer system for maintaining cache coherence, the computer systemcomprising: a teleporter configured to indicate a cache hit; a firstdestination storage location; and a destination endpoint coupled to theteleporter and the first destination storage location, the destinationendpoint configured to: based at least on receiving an indication of thecache hit from the teleporter, check cache coherence; and based at leaston detecting a lack of coherence, perform a reactive remediation processusing a data block in the first destination storage location.
 10. Thecomputer system of claim 9, wherein the remediation process comprises:replacing, as a cached data item, a data block indicated by the cachehit with a replacement data block that triggered the cache hit.
 11. Thecomputer system of claim 9, wherein receiving, at the destinationendpoint, the indication of the cache hit from the teleporter comprises:receiving, from the teleporter, a data hash value and a matching blocklocation; and wherein checking cache coherence comprises: generating acheck hash value for a data block found at the matching block location;and comparing the check hash value with the data hash value.
 12. Thecomputer system of claim 11, wherein the data hash value comprises a256-bit hash.
 13. The computer system of claim 11, wherein the checkhash value comprises a 256-bit hash.
 14. The computer system of claim11, wherein the destination endpoint is further configured to: based atleast on the check hash value matching the data hash value, copy thedata block found at the matching block location to a second destinationstorage location; and based at least on the check hash value notmatching the data hash value, copy a data block received from a sourceendpoint to the second destination storage location.
 15. The computersystem of claim 11, wherein the remediation process comprises: promotingthe data hash value from a short-term cache to a long-term cache.
 16. Anon-transitory computer storage medium having computer-executableinstructions that, upon execution by a processor, cause the processor toat least perform operations to maintain cache coherence, the operationscomprising: receiving, at a destination endpoint, an indication of acache hit from a teleporter; based at least on receiving the indicationof the cache hit, checking cache coherence; and based at least ondetecting a lack of coherence, performing a reactive remediation processusing a data block in a first destination storage location.
 17. Thenon-transitory computer storage medium of claim 16, wherein theremediation process comprises: replacing, as a cached data item, a datablock indicated by the cache hit with a replacement data block thattriggered the cache hit.
 18. The non-transitory computer storage mediumof claim 16, wherein receiving, at the destination endpoint, theindication of the cache hit from the teleporter comprises: receiving,from the teleporter, a data hash value and a matching block location;and wherein checking cache coherence comprises: generating a check hashvalue for a data block found at the matching block location; andcomparing the check hash value with the data hash value.
 19. Thenon-transitory computer storage medium of claim 18, wherein the datahash value comprises a 256-bit hash, and wherein the check hash valuecomprises a 256-bit hash.
 20. The non-transitory computer storage mediumof claim 18, wherein the computer-executable instructions further causethe processor to perform operations comprising: based at least on thecheck hash value matching the data hash value, copying the data blockfound at the matching block location to a second destination storagelocation; and based at least on the check hash value not matching thedata hash value, copying a data block received from a source endpoint tothe second destination storage location.
 21. The non-transitory computerstorage medium of claim 18, wherein the remediation process comprises:promoting the data hash value from a short-term cache to a long-termcache.